The present invention relates to a fixing device and an image forming apparatus.
In a conventional image forming apparatus such as a printer, a copier, and a facsimile, an image is formed through the following process. First, a charge roller charges a surface of a photosensitive drum. An exposure device such as an LED head exposes the surface of the photosensitive drum to form a static latent image or a latent image thereon. A developing roller attaches a thin layer of toner to the static latent image to form a toner image. A transfer roller transfers the toner image to a sheet. A fixing unit or fixing device fixes the toner image to the sheet before discharging the sheet.
Patent Reference has disclosed a conventional fixing device of a belt nip type. The conventional fixing device is provided with a pressing pad pressed against a fixing roller or a fixing member through a pressing belt.
FIG. 2 is a schematic sectional view showing the conventional fixing device. As shown in FIG. 2, a fixing device 101 includes a pressing belt assembly 102; a fixing roller 103 facing the pressing belt assembly 102; a pressing belt 105; a pressing pad 106; a spring 107 for urging the pressing pad 106 against the fixing roller 103 through the pressing belt 105; a holder 108 for holding the pressing pad 106; and a heater 111.
In the fixing device 101, the holder 108 is guided with a guide member (not shown) to freely slide back and forth. A nip portion n is formed between the pressing belt assembly 102 and the fixing roller 103. After a toner image is transferred to a sheet, when the sheet passes through the nip portion n, the fixing roller 103 heats the toner image and the pressing belt assembly 102 applies pressure to the toner image, so that the toner image is fixed to the sheet.
Patent Reference Japanese Patent Publication No. 09-34291
In the conventional fixing device 101, when the pressing belt 105 moves, an inner circumferential surface of the pressing belt 105 slides against an upper surface of the pressing pad 106, thereby causing frictional resistance. Accordingly, the pressing pad 106 may be inclined, vibrate, or wobble, so that the holder 108 may seize the guide member. As a result, it is difficult to stably press the pressing pad 106 against the fixing roller 103, thereby causing distortion, shift, or irregularity in an image, and lowering image quality.
In view of the problems described above, an object of the present invention is to provide a fixing device and an image forming apparatus capable of solving the problems of the conventional fixing device. In the fixing device, it is possible to stably press a pressing pad against a fixing member, thereby improving image quality.
Further objects and advantages of the invention will be apparent from the following description of the invention.